JPH0771868B2 - Optical recording medium - Google Patents

Description

The present invention relates to a novel high-sensitivity and high-density optical recording medium capable of recording / reproducing information using laser light.
More specifically, it is suitable for recording / reproducing information by utilizing the change in reflectance or transmittance caused by the deformation or removal of the portion irradiated with laser light, which is a high-density energy beam, due to melting, decomposition, etc. And a heat mode optical recording medium.

[Conventional technology]

In optical recording using a laser beam, since the writing or reading heads are not in contact with each other, the recording material is characterized by not being worn and deteriorated. Therefore, various optical recording materials have been researched and developed. In particular, in the fields of optical discs, laser printers, facsimiles, etc., many optical information recording materials using laser light are known. As a typical example thereof, it is known to use a metal-based substance found in metals, alloys, or oxides such as Te, Bi, In, and Ge in the recording layer as a light absorbing substance. However, since the metallic substance has high thermal conductivity and melting point as well as high surface reflectance, it has a drawback that the energy of laser light cannot be effectively used. In addition, these metal-based materials have a serious problem in terms of toxicity.

On the other hand, as an optical recording material other than the above-mentioned metal-based materials, it is also known to use an organic dye such as fluorescein, Sudan Black B, Congoled, Sudan Blue, Rhodamine 6G as a light absorbing substance in the recording layer (for example, Japanese Patent Application Laid-Open No. 2000-242242). Akira
56-55289 and Japanese Patent Publication No. 57-209191).

Generally, the thermal conductivity of organic substances is as small as 1/10 to 1/100 of that of metals, so not only the heat generated by photothermal conversion can be effectively used, but also the dissipation of heat in the horizontal direction is reduced, It becomes possible to record faithful signals, that is, high density recording. However, since these known organic substances mainly show absorption in the visible light region, the recording laser light source is limited to Ar ⁺ laser (488 nm) or He-Ne laser (633 nm), and the near infrared light region (~ It has an oscillation wavelength of 800nm) and is not suitable for recording by a semiconductor laser that can reduce the size and weight of the entire device.

Cyanine dyes and the like are known as organic compounds exhibiting absorption in the near infrared region, for example, in JP-A-58-114989.
However, since the cyanine dye has poor stability to moisture, oxygen, light, etc., it has a drawback that the recording state cannot be kept stable.

[Problems to be solved by the invention]

As described above, conventionally proposed organic optical recording materials do not have sufficient light absorption ability or light reflection ability, or have problems in durability, storage stability, etc. At present, there is nothing that satisfies the performance.

As a result of extensive research, the present inventors have found a group of metal complexes of monoazo compounds having a large molecular extinction coefficient in the visible light and near infrared light regions. When the recording layer containing the metal complex was irradiated with laser light, photothermal conversion was efficiently caused, and it was acknowledged that the portion irradiated with laser light had a large change in reflectance or transmittance. Ivy. (Japanese Patent Application No. 60-297944).

The present invention has been made for the purpose of further improving the above invention.

[Means for solving problems]

The present inventors have made the recording material containing the metal complex group of the preceding invention extremely stable by providing a protective layer made of an organic polymer, particularly a protective layer having a certain thickness or more. The present invention has been confirmed to be improved, and the present invention has been achieved.

That is, the optical recording medium of the present invention basically comprises a support, a recording layer and a protective layer, and the recording layer contains a metal complex of a monoazo compound represented by the following general formula (1), and The protective layer is an organic polymer.

(In the formula, X is a residue which forms a heterocyclic ring which may be substituted with an electron-donating group or an electron-withdrawing group together with a nitrogen atom and a carbon atom to which it is bonded, and Y Is
A residue which, together with the two carbon atoms to which it is attached, forms an aromatic ring which may be substituted by electron-donating groups. Z is a hydroxyl group or a carboxyl group. ) In the above formula, the electron donating group is monomethylamino,
Lower monoalkylamino groups having up to 4 carbon atoms such as monoethylamino, dimethylamino, diethylamino, di-n-
Examples include lower dialkylamino groups having up to 4 carbon atoms such as butylamino, lower alkoxy groups having up to 4 carbon atoms such as methoxy and ethoxy, lower alkyl groups having up to 4 carbon atoms such as methyl and ethyl, amino groups and hydroxyl groups. . The alkyl moiety may be sulfonated, for example. Preferred electron-donating groups are a dimethylamino group, a diethylamino group, a hydroxyl group, a methoxy group or a methyl group when Z is a hydroxyl group, and a dimethylamino group, a diethylamino group or a hydroxyl group when Z is a carboxyl group.

On the other hand, examples of the electron-withdrawing group include a halogen atom such as chlorine and bromine, a nitro group, a cyano group, a trifluoromethyl group and a carboxyl group. Preferred electron withdrawing groups are chlorine, bromine or nitro groups.

These substituents may be one kind or two kinds.

Examples of the heterocycle include pyridyl, thiazolyl, benzothiazolyl, quinolyl, pyrimidyl, hydroxybenzothiazolyl, and other heterocycles. Preferred heterocycles are thiazolyl and benzothiazolyl. On the other hand, examples of the aromatic ring include phenyl and naphthyl. When a benzene ring is selected as the aromatic ring, it is preferably substituted with the electron donating group. The electron-donating group has an auxiliary color effect and an effect of increasing the stability of the complex.

Representative examples of the monoazo compound forming a complex in the present invention include the following when Z is a hydroxyl group.

1) Thiazolylazo compounds.

2) Hydroxybenzothiazolylazo compound.

3) Benzothiazolylazo compounds.

4) Pyridylazo compounds.

5) Quinolylazo compounds.

6) Pyrimidylazo compounds.

The following are typical examples when Z is a carboxyl group.

1) Thiazolylazo compounds.

2) Benzothiazolylazo compounds.

3) Pyridylazo compounds.

These compounds are described, for example, in Analytical Chemistry, Vo1.11, P621-P62.
8 (1962) and Nippon Chemistry Magazine, Vol. 83, No. 11, P1185-P1
It is synthesized according to the method described in 189 (1962).

In the present invention, the metal forming a complex with a monoazo compound is not particularly limited as long as it is a metal capable of forming a complex with the monoazo compound, but iron, cobalt, and an iron group element selected from nickel are particularly good, A copper group element selected from copper, iron and gold is also used. Complexes composed of these metals generally have an absorption maximum wavelength on the longer wavelength side than the absorption maximum wavelength of the monoazo compound itself, and at the same time, its molecular absorption coefficient (ε) increases, so that it efficiently absorbs the recording laser light and It is preferably used because it causes conversion. Particularly, a complex in which divalent iron is selected as a metal has a maximum absorption wavelength in a long wavelength region and has a large molecular absorption coefficient in a semiconductor laser oscillation wavelength region, and is practically useful.
The attribution of this characteristic absorption band is not always clear, but it is considered to be a problem for iron → ligand type charge transfer.

The ratio of the monoazo compound and the coordination metal used in the present invention is usually stoichiometrically set to 1/1, 2/1, etc., but in some cases the optical properties of the product may be greatly affected. It is desirable to select an appropriate ratio according to

The metal complex of the monoazo compound used in the present invention is synthesized by any method. For example, it can be obtained by reacting one or more kinds of the monoazo compound represented by the formula (I) with one or more kinds of metal salts in water and / or an organic solvent.

Examples of the metal salt used in the synthesis of the metal complex include chloride, hydroxide, nitrate, sulfate, and phosphate of the target metal.
Examples thereof include ammonium sulfate, oxalate, perchlorate, acetate, formate, carbonate, stearate, borate and the like.

The recording layer in the optical recording medium of the present invention is composed of the metal complex of the monoazo compound alone or in combination with other materials, and is made of an inorganic material such as glass, aluminum or ceramics, or a synthetic resin such as polymethylmethacrylate, polycarbonate or polyester. It is provided on a support made of material. The support is transparent or opaque, and a support having optical characteristics suitable for each of the incident directions of the recording and reproducing laser light is used. In particular, when incident from the transparent support surface side, recording / reproduction can be performed without being affected by defects such as dust or scratches adhering to the surface, and therefore it is more preferably used. It is also possible to use a so-called air-sand Germany type recording material in which two disk-shaped transparent supports provided with recording layers are arranged so that their recording layer surfaces are located inside and are bonded so as to have voids. The shape of the support can be selected according to the purpose of use, and examples thereof include a disk shape, a tape shape, and a sheet shape. Particularly, in the case of a disk shape, a pregroup is provided to facilitate tracking mainly. May be.

Further, the metal complex used in the recording layer may be composed of two or more kinds of monoazo compounds and / or metal elements as necessary, and by mixing them, the laser light absorption wavelength is selected or adjusted. It is also possible.

These recording layers can be formed by a vacuum vapor deposition method, or by dissolving the metal complex alone or in combination with another material such as a resin in a suitable solvent, and using a simple method such as a spin coating method, a dipping method, a bar code method, or a cast method. It can be formed by any coating method. In this case, in the latter case, a stabilizer, a surfactant, a dispersant, a leveling agent, etc. may be used as required.

The thickness of the recording layer formed is preferably 10 to 500 nm, and at the same time, the transmittance for recording laser light is preferably 70% or less. When the transmittance is more than 70%, it does not have sufficient light absorption ability or light reflection ability.

The resin used in combination with the above is preferably thermoplastic or self-oxidizing resin, polycarbonate,
Polymethylmethacrylate, polystyrene, polyethylene, polyethylene oxide, polyvinyl butyral,
It is possible to appropriately select from a wide range of resins such as polyvinyl acetate, nitrocellulose, polyvinyl alcohol, and methyl cellulose. Nitrocellulose is particularly preferable because it has a strong oxidizing action. The weight ratio of the organometallic complex to the resin is generally 0.1% or more, preferably 10%
More preferably, it is 30% or more. Too little,
In some cases, sufficient light absorption capacity or optical density difference may not be obtained.

An organic polymer is used as the protective layer used in the present invention. The organic polymer can be formed by a wet method such as a spin coating method which does not require an expensive vacuum system, is economical and has a certain thickness or more, so that the metal complex of the recording layer can be formed. It has the features of controlling the crystal growth and reducing the increase in noise level during playback. In general, the effect occurs when the film thickness is 0.01 μm or more, preferably 0.1 μm or more, and particularly preferably 0.5 μm or more.
The upper limit of the film thickness is not particularly limited, but about 50 μm is sufficient, and it may be 100 μm in some cases. Usually, it is preferably used in the range of 0.5 μm to 25 μm.

The organic polymer used is widely used as long as it can be imparted without impairing the smoothness of the recording layer. For example, polyisobutylene, poly4-methylpentene-1, polyethylene, polyolefin such as polypropylene, olefin-based copolymers of olefin and vinyl acetate, maleic anhydride, acrylic acid, acrylic resin such as butyl methacrylate, polyacrylonitrile, Examples include polyamide, polyester, polyvinyl acetate, polyurethane, polyether, polycarbonate, silicone resin and the like. When applied by spin coating, hexane,
Polymer soluble in solvents with low dielectric constant such as cyclohexane,
For example, polyisobutylene, polyisobutyl metal acrylate, cyclized polyisoprene, etc. are preferably used. The addition-polymerization type silicone rubber is used particularly preferably because it is used without solvent and does not dissolve the metal complex in the recording layer.
It is also recognized that the resin having a larger contact angle with water improves the stability of the recording medium. 70 ° or more, preferably
A polymer having a contact angle of 80 ° or more, particularly preferably 90 ° or more is preferably used.

The optical recording medium of the present invention basically comprises a support 10, a recording layer 20 and a protective layer 40 as shown in FIG. The recording or reproducing laser light is indicated by arrows 100 or 200. If necessary, an undercoat layer 30 can be provided on the support as shown in FIG. Nitrocellulose is particularly preferable for the undercoat layer. Further, as shown in FIG. 3, it is also possible to provide a reflective layer 50 made of a metal such as Al, Ag, Au or a transparent dielectric layer 60 made of SiO ₂ , Si ₃ N ₄ or the like. Generally, when providing a metal reflection layer, not only further steps such as a vacuum deposition method are required, but also the optical characteristics of the optical recording medium due to repeated reflection greatly depend on the film thickness of the recording layer. The thickness needs to be tightly controlled. The optical recording medium of the present invention has a feature that the reflectance or the change in reflectance required for recording / reproducing can be obtained without providing a metal reflection layer.

Information recording is performed by irradiating an optical recording medium with a laser beam having a high energy density to cause a chemical change or a physical shape change in a part of the recording layer. That is, recording is carried out by deforming or removing the portion irradiated with the laser beam, which is melted, decomposed, or the like by the heat generated through the photothermal conversion. The pits formed by the laser light can be formed with low energy, and the beam diameter of the laser light is 1 μm.
When condensed to about m, the pits are preferably formed with a power of 1 to 10 mW on the surface of the recording layer and an irradiation time of 50 to 500 nsec.

On the other hand, in the reading of information, the output is attenuated to 1/5 to 1/10 of that at the time of recording, and the low-output laser light set so that the recording layer does not cause a chemical change or a physical shape change is used as continuous light. This is done by irradiating and detecting a change in the reflected light amount or the transmitted light amount depending on the presence or absence of a pit. Usually, it is preferable to detect by reflected light that can be recorded / reproduced by a single optical system.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

All parts in the examples represent parts by weight. The monoazo compounds used in the examples are represented by the abbreviations mentioned above.

Example 1 An iron complex was obtained by adding 1/2 equivalent of a ferrous ammonium sulfate aqueous solution to a 1,4-dioxane solution of TAM, adjusting the pH, and extracting with chloroform. The complex has λmax of 760 nm and ε of 2.7 × 10 ⁴ · mol ⁻¹ · cm ^{−1 in} chloroform.
Showed absorption of.

Meanwhile, nitrocellulose (viscosity 1/2 second, nitrogen content 12%)
The DMF solution dimethylformamide of was filtered through a 3 μm membrane filter and then spin-coated on PMMA (polymethylmethacrylate) disk to give a dry film thickness of 0.8 μm.
m undercoat layer was provided. Next, a chloroform solution of an iron complex was prepared, filtered through a 0.2 μm membrane filter, and then spin-coated on the above disk to obtain a dry film thickness of 55 nm.
The recording layer of Further, a cyclohexane solution of polyisobutylene was similarly applied by a spin coating method to form a protective layer having a dry film thickness of 5 μm.

FIG. 1 schematically shows the optical recording medium manufactured in this way. The optical recording medium in which the recording layer 20 and the protective layer 40 are provided on the PMMF substrate 10 is rotated at a linear velocity of 11 m / sec, and the arrow 1
A semiconductor laser beam having an oscillation wavelength of 780 nm was condensed from a direction of 00 to a beam diameter of 1.2 μm and irradiated in pulses.

In this case, the irradiation power of the laser beam was 6 mW, the pulse width was 500 nsec, and the duty ratio was 50%. Next, 1 mW of semiconductor laser light was radiated as continuous light onto the recording pit train rotating under the same conditions, and when the signal was reproduced by changing the reflected light intensity, a CNR of 50 dB was obtained. on the other hand,
When recording / reproduction was performed from the recording film surface side to the sample similarly prepared, a good reproduction signal was obtained. When this optical recording medium was left in an environment of 40 ° C. and 95% RH for 100 hours and then reproduced, the CNR was 48 dB, which was stable without any substantial decrease.

A good reproduction signal was obtained even when a He—Ne laser beam with an oscillation wavelength of 633 nm was used under the same conditions in place of the semiconductor laser.

Examples 2 to 4 In Example 1, an optical recording medium was produced by changing the type of polymer used for the protective layer and the thickness of the protective layer. The results are shown in Table 1 together with Example 1. It can be seen from Table 1 that by providing the protective layer, stabilization of recording characteristics is achieved.

According to the observation with a reflection optical microscope, in the control example in which the protective layer is not provided, the crystallization of the recording layer occurs after standing for 100 hours, which causes the scattering of the laser light at the time of reproduction, resulting in the noise level. Seems to have risen. It should be noted that, even after the optical recording medium having stable recording characteristics was left for 100 hours, no change in the state due to crystallization of the recording layer was observed in both the recorded portion and the unrecorded portion.

[Brief description of drawings]

1 to 3 are sectional views showing the structures of various embodiments of the optical recording medium of the present invention. In the figure, 100 and 200 denote incident directions of recording or reproducing laser light. Further, 10 is a support, 20 is a recording layer, 30 is an undercoat layer, 40 is a protective layer, 50 is a reflective layer, and 60 is a transparent dielectric layer.

Front Page Continuation (72) Inventor Shiro Nagata Kuraray Co., Ltd., a 1-share company at 2045 Aoyama Sakata, Kurashiki City, Okayama Prefecture (56) References JP 62-30090 (JP, A) JP 63-9577 ( JP, A) JP 63-9579 (JP, A) JP 59-11385 (JP, A)

Claims (15)

[Claims] 1. A recording medium comprising a support, a recording layer and a protective layer, the recording layer having the general formula (In the formula, X is a residue which forms a heterocyclic ring together with the nitrogen atom and carbon atom to which it is bonded, and Y is
A residue that, together with the two carbon atoms to which it is attached, forms an aromatic ring. Z is a hydroxyl group or a carboxyl group. ) An optical recording medium containing a complex of a monoazo compound represented by the formula (3) and a metal, and the protective layer is an organic polymer. 2. The optical recording medium according to claim 1, wherein the protective layer has a thickness of 0.01 μm or more. 3. The heterocyclic ring is substituted with at least one electron-donating group or electron-withdrawing group, or the aromatic ring is substituted with at least one electron-donating group. The optical recording medium according to the second aspect. 4. The optical recording medium according to claim 2, wherein the heterocycle is a heterocycle selected from the group consisting of thiazolyl, benzothiazolyl, pyridyl, quinolyl, pyrimidyl and hydroxybenzothiazolyl. 5. The optical recording medium according to claim 2, wherein the aromatic ring is phenyl or naphthyl. 6. The optical recording medium according to claim 3, wherein the electron-donating group is one or more groups selected from an alkyl group and an alkoxyl group. 7. The optical recording medium according to claim 3, wherein the electron-donating group is one or more groups selected from the group consisting of an amino group, a substituted amino group and a hydroxyl group. 8. The optical recording medium according to claim 3, wherein the electron-withdrawing group is one or more groups selected from the group consisting of a halogen atom, a nitro group, a cyano group and a trifluoromethyl group. 9. The optical recording medium according to claim 2, wherein the recording layer is composed only of a complex of a monoazo compound and a metal. 10. The organic polymer forming the protective layer is a polymer having a contact angle to water of 70 ° or more.
Item 10. The optical recording medium according to any one of items 9 to 9. 11. The optical recording medium according to any one of claims 1 to 9, wherein the organic polymer forming the protective layer is polyisobutylene, polyisobutyl methacrylate or cyclized polyisoprene. 12. The optical recording medium according to claim 2, wherein a reflective layer is provided between the substrate and the recording layer. 13. The optical recording medium according to any one of claims 2 to 11, wherein a reflective layer is provided on the recording layer. 14. The optical recording medium according to claim 12, wherein a transparent dielectric layer is provided between the reflective layer and the recording layer. 15. The optical recording medium according to any one of claims 2 to 11, wherein an undercoat layer is provided between the substrate and the recording layer.